COMMISSION 27 OF THE I. A. U.
        INFORMATION BULLETIN ON VARIABLE STARS
                    Number 1778

                                   Konkoly Observatory
                                   Budapest
                                   1980 May 5


  ULTRAVIOLET OBSERVATIONS OF THE SILICON STAR HD 179 761


Between July 21 and August 15, 1979 I obtained photoelectric observations on
the silicon star HD 179 761 (Searle and Sargent, 1964) at the Shemakha
Observatory, Azerbaijan SSR. The one-channel integrating photometer was
attached to a 35-cm Cassegrain telescope. The 18 measurements of this star
were made in ultraviolet light with a FEU79 photomultiplier and UG1 2 mm
filter, close to the U band of the UBV photometric system.

HD 180 482 (C1) and HD 179 343 (C2) served as comparison stars. The
differential magnitudes have been obtained by averaging the results of five
measurements of the program and comparison stars, made in the order of C1 - PR
-C2. The standard deviation between the averaged and individual values of the
differential magnitudes was less than 0.008m at every night.

The differential magnitudes corrected for the extinction in usual way, are
given in instrumental system in Table I.

Table I

J.D.         PR-C1    PR-C2    PR-(C1+C2)/2
2444000+
76.295     -1.019    -2.114       -1.566
78.312     -1.028    -2.125       -1.576
79.250     -1.009    -2.110       -1.559
80.303     -1.036    -2.127       -1.581
81.297     -1.019    -2.121       -1.570
83.236     -1.018    -2.119       -1.568
84.268     -1.022    -2.114       -1.568
85.275     -1.023    -2.123       -1.572
88.238     -1.010    -2.113       -1.561
90.281     -1.025    -2.120       -1.572
92.316     -1.039    -2.126       -1.582
94.355     -1.024    -2.117       -1.570
95.243     -1.023    -2.116       -1.569
96.261     -1.021    -2.122       -1.575
97.249     -1.035    -2.125       -1.579
99.231     -1.043    -2.130       -1.586
100.246    -1.030    -2.125       -1.577
101.236    -1.018    -2.118       -1.567

The period of light variation of HD 179 761 is determined by the method of
Fourier analysis of unequally spaced data (Deeming, 1975), using a small
computer KSR 4100 of the Astrophysical Observatory at Potsdam. The value of
the period is found to be 1.73d+-0.01d in agreement with the result of
Stepien (1968), who observed this star in UBV photometric system and found a
period of 1.71d.

The observations are plotted against phase calculated with the period P=1.73d
in Figure 1.

                                [FIGURE 1]

   Figure 1. The differential magnitudes of HD 179761 - (C1+C2)/2
   plotted against phase (Hel.Max.=J.D. 2444099.23+E*1.73d)


B. VETO
Department of Astronomy of Eotvos University,
Budapest, Hungary
Visiting astronomer at Astrophysical Observatory, Potsdam, GDR

References :

Deeming, T.J. 1975, Astrophys. and Space Sci. 36, 137 [BIBCODE 1975Ap&SS..36..137D ]
Searle, L. and Sargent, W.L. 1964, Astrophys. J. 139, 793 [BIBCODE 1964ApJ...139..793S ]
Stepien, K. 1968, Astrophys. J. 154, 945 [BIBCODE 1968ApJ...154..945S ]